Characterization of the surface film on Zr-based bulk metallic glass using X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM)

Using XPS, we have for the first time studied the release of metal ions in the film of the Zr-based bulk metallic glass to the corrosive solutions during immersing. The composition of Al ions in the film of the as-cast metallic glass (41%) is substantially higher than the nominal Al composition of the alloy (9.5%). We proposed that the enriched Al ions can be attributed to the preferential oxidation of Al atoms. After immersing in the NaCl- and HCl-solution, the composition of Al ions in the films decreases from 41% to 28.09% and 21.76%, respectively. This indicates that some of the Al ions in the film are dissolved into the solution during immersion. The composition changes of metal ions in the film of the immersed alloys relative to those of the as-cast metallic glass were discussed using the point defect model. SEM was also used to examine the surface morphology of the samples. No pit corrosion was observed in the SEM images of the immersed metal glass.

► In this study, we have made four interesting observations.
► First, the composition of Al metal ions in the film of the as-cast metallic glass (41%) is much higher than the nominal Al composition of the alloy (9.5%).
► We suggest that this should be attributed to the preferential oxidation of Al atoms.
► Second, the composition of Al ions in the film of the immersed metallic glass decreases significantly, indicating that the toxic Al oxide and Al ions in the film are dissolved into the solutions during immersion.
► Third, the concentration of Cl− ions has no significant effect on the compositions of metal ions in the film.
► Fourth, the composition of Zr ions dominates in the film of the immersed metallic glass, indicating that the ZrO2 oxide in the film is very hard to get corroded in the corrosive solutions.